For

light, slim, status meter on back

Against

Still makes iPhone massive, only works for iPhone 5,

The Mophie helium for iPhone is a new dedicated juice pack for the iPhone, sitting snugly around the Apple smartphone and promising to deliver power when your phone starts to run low. We fitted the new exterior battery case to our iPhone 5 to see if it really is that easy.

Design

As with previous Mophie cases, the gunmetal metallic helium comes in two parts that spilt to neatly fit around your iPhone 5, making it easy to fit and take off whenever needed. The locking mechanism - which snaps into place - is strong, but not so much that you won't be able to get the thing off when you want to.

Once on, the case does of course add bulk and length to your phone, but not overly so. If you've previously seen the company's iPhone 4 and 4S offerings the helium is 13 per cent thinner. To give you an idea of size and design, think of the curved iPhone 3GS and you'll be on the right track.

Made from a smooth soft-touch material, the helium is solid, well built and comfortable to hold. The iPhone 5 buttons are still easily accessible, although the lightning connector is replaced on the outside with a micro USB socket. You'll also need to make sure your headphones jack has a long straight connector, if it doesn't it won't fit any more. The good news is, an adapter is provided in the box.

Around the back there are four LED lights that act as a power indicator, to let you know how much charge you have, and a toggle on/off switch to set the helium going. It's all very similar to the company's Samsung Galaxy S case we recently reviewed.

Performance

Giving you an extra boost during the day is what the helium is all about. It's also Mophie's thinnest and lightest juice pack to date and packs 80 per cent more battery life into its case than previous models. It has a 1500mAh battery which is almost the same capacity as the iPhone 5's internal battery, and that should give you more than enough power to extend your iPhone battery by another day at least.

Mophie promise helium users will get up to six additional hours of talk time, 30 additional hours of audio playback, seven additional hours of video playback or seven hours of Wi-Fi internet use (six hours with 3G and LTE) by recharging their phone from the accessory.

Charging performance is good, giving us 50 per cent of battery charge in just under an hour and certainly living up to the claims of plenty of extra power.

It's also worth noting that the helium comes with three-quarters charge when you buy it, handy if you need the power there and then.

Annoyances

No matter how you cut it, the Mophie helium will still add plenty of weight, bulk and length to that shiny new Apple iPhone you've just bought.

Yes it acts as a case, yes you'll get longer battery life from it, and yes it will keep your phone protected, but you do have to pay for that with the increased size of the device.

Additionally, because this is a dedicated power case for the iPhone 5, you can't use it to charge other devices you might have, like your tablet, a Mi-Fi, certain cameras, or other gadgets in the depths of your bag.

Furthermore, while there are some advantages to having a micro USB charging socket, it would be nice to have a Lightning adapter option so you could plug the phone into a docking speaker or use the Apple cable with, or without, the helium case.

Verdict

The Mophie helium does the best job it can, and is likely to be popular among heavy users who want a dedicated iPhone 5 battery case, rather than something that can be used on other devices. We quite like that you can charge your phone and the case at the same time.

That said, the helium still isn't perfect, not from what it delivers, but just by the nature of the adversities it has to overcome. If you don't mind doubling the size of your iPhone 5, then the helium is great; if not, then this isn't for you.